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This is the final highway accident report (NTSB-HAR-71-1) from the National Transportation Safety Board, adopted in December 1970. It covers the collapse of the U.S. 35 bridge between Point Pleasant, West Virginia, and Kanauga, Ohio, on December 15, 1967, which killed 46 people. The Board found that the cause was a cleavage fracture in eyebar 330 at joint C13N. That fracture grew from a flaw produced over 40 years by stress corrosion and corrosion fatigue, in a spot that could not be seen or found by inspection.
“Cooper”1 page
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and Masters, has been described in Section III C of this report. The final paragraph of that report reads as follows:
"In summary, it was agreed that the small oxide-covered crack which led to the rapid fracture of eyebar No. 330, similar nearby secondary cracks, and similar cracks in other eyebars were produced by a corrosion process. There is supporting evidence that either stress-corrosion cracking or corrosion-fatigue could be this corrosion process although the limited data obtained to date are not sufficient to draw a definite conclusion. In view of the fact that no further eyebars with cracks are available, fracture studies to more clearly establish the mechanism of the crack propagation are not possible."
Subsequent to this report, the U. S. Steel laboratory used a special picric acid etch to bring out the grain boundaries more clearly in a portion of the fracture in eyebar No. 330. An example of the result is shown in Figure 33a and 33b. In the right photograph, the appearance of the specimen after etch is shown. In the left photograph, the grain boundaries detected by the investigator have been marked on an overlay. This crack is clearly transgranular rather than intergranular, favoring the mechanism of corrosion-fatigue.
The evidence supporting stress corrosion cracking is as follows:
(a) Continuous high stress intensity at or about the yield strength of the material.
(b) Probable concentration of corrosive agents such as hydrogen sulfide or salts in a confined space, as indicated by the presence of the elements sulfur and chlorine on the crack face, particularly near the mouth of the crack.
(c) Some intergranular cracking is present.
(d) The material showed susceptibility to $ \mathrm{H}_{2} \mathrm{S} $ stress-corrosion cracking under concentrated, controlled conditions at stress levels as low as 15,000 psi.
(e) Range of stress (live load) was small, probably about 15,000 psi.
The evidence supporting corrosion-fatigue is as follows:
(a) Some cracks in eyebar No. 330 are definitely transgranular. Document, cited by the archive. The PDF is mirrored here; the original link is above. The text was read from the page images by GLM-OCR; expect the odd misread word. 202 pages are in the text index: search them above, or from the library's search.